Rate control device and method for CDMA communication system

ABSTRACT

A traffic channel transmission device for a CDMA communication system using a plurality of coding rates and orthogonal codes, determines a present channel condition and adaptively selects a coding rate and an orthogonal code according to the determination. In the device, a channel receiver receives a channel signal and a controller analyzes the received signal to decide an environment of a channel in service and generates a coding rate select signal and orthogonal code information according to the decision result. A channel transmitter includes a channel encoder for encoding transmission data at a coding rate selected according to the coding rate select signal and an orthogonal modulator for generating an orthogonal code according to the orthogonal code information to spread the encoded data with the generated orthogonal code, whereby the channel transmitter adaptively encodes and spreads the transmission data according to the channel environment. The orthogonal code information includes a number and a length of the orthogonal code.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to communication systems,and in particular, to an apparatus and method for adaptively controllinga channel data rate according to a channel environment in a CDMAcommunication system.

[0003] 2. Description of the Related Art

[0004] At present, CDMA (Code Division Multiple Access) communicationsystems are implemented in accordance with the IS-95 Standard. With theprogress of mobile communication technology, the number of mobilecommunication service subscribers is increasing and demands for variousservices are rising in proportion to the increased user demand. To datemany methods have been proposed to meet the subscribers' demands.

[0005]FIG. 1 illustrates a structure of a forward traffic channeltransmission device for the CDMA communication system, wherein thetraffic channel includes a fundamental channel and a supplementalchannel.

[0006] Referring to FIG. 1, a channel encoder and puncturing part 10encodes and punctures input data and outputs symbol data. Aconvolutional encoder or a turbo encoder can be used for the channelencoder and puncturing part 10. A symbol repetition part 20 repeats therespective encoded symbol data for the input data having different bitrates to output a single common symbol rate. An interleaver 30interleaves an output of the symbol repetition part 20. A blockinterleaver can be used for the interleaver 30.

[0007] A long code generator 91 generates long codes for the useridentification, which are uniquely assigned to the respectivesubscribers. A decimator 92 decimates the long codes so as to match arate of the long codes to a rate of the symbols output from theinterleaver 30. A mixer 40 mixes the encoded symbols output from theinterleaver 30 with the long codes output from the decimator 92.

[0008] A signal mapping part 50 maps binary data output from the mixer40 into 4-level data by converting data “0” to “+1” and data “1” to“−1”. An orthogonal modulator 60 modulates data output from the signalmapping part 50 with an orthogonal code. A Walsh code can be used forthe orthogonal code. In this case, Walsh codes of lengths 64, 128 and256 bits can be used. A spreader 70 spreads the orthogonal modulationsignal output from the orthogonal modulator 60 by combining it withspreading sequences. PN (Pseudo-random Noise) sequences can be used forthe spreading sequences. Accordingly, a QPSK (Quadrature Phase ShiftKeying) spreader can be used for the spreader 70. A gain controller 80controls a gain of the spread signal input from the spreader 70according to a gain control signal Gc.

[0009] In operation, when the convolutional encoder is used for thechannel encoder and puncturing part 10, the coding rate is ⅓ and theconstraint length, k=9, for an IS-95 system. Therefore, one input databit is encoded into three encoded bits (i.e., three symbols) in thechannel encoder and puncturing part 10 (which performs ⅓ rateconvolutional encoding or ⅓ rate forward error correction (FEC)).Forward error correction is utilized to provide coding gain to a channelso as to compensate for an increase in a BER (Bit Error Rate) at amobile station (for the case of a forward link) and a base station (forthe case of a reverse link). An increase in the BER of a channel mayarise as a result of the channel having a reduced SNR (Signal-to-NoiseRatio) due to an increase in signal path loss, noise and interference.

[0010] It is well known that CDMA communication systems cannot providereliable communication service when a mobile station is located at anouter service area of the base station or is in a bad channelenvironment. In this case, it is preferable to change the coding rate toenhance the quality of the communication service in the bad channelenvironment. That is, when the channel SNR is reduced due to a badchannel environment or an increased distance between a mobile stationand a base station, it is preferable to use a coding rate (or FEC rate)lower, ⅙ for example, than the present coding rate of ⅓.

[0011] In particular, when the distance between the base station and themobile station increases, a reception device is very susceptible to pathloss or noise on the link channel and interference, so that the channelSNR is reduced unless a transmission device increases the transmissionpower or performs a pertinent compensation. Therefore, when the trafficchannel transmission device with the fixed channel structure of FIG. 1experiences an increased BER (Bit Error Rate) due to a reduction in SNR,the base station increases a forward link traffic power in order tocompensate for the increase in the BER. Therefore, it is preferable touse the FEC with a lower coding rate than the FEC in use. Given a ⅓coding rate it has been shown that channel gain is lower by about 0.2-1dB as compared with a ⅙ coding rate. For example, the forward receptionpower of a mobile station using the ⅓ coding rate is lower by about 1 dBthan that of a mobile station using the ⅙ coding rate, when the mobilestation is far from the base station or in a bad forward channelenvironment. Therefore, the base station should increase the forwardlink transmission power, resulting in a waste of transmission power andlow communication performance.

[0012] Unlike the channel transmission device with the fixed channelstructure of FIG. 1, a channel transmission/reception device for a 3rdgeneration multicarrier CDMA system as proposed in the TIA/EIA TR45.5conference, includes a scheme for transmitting and receiving therespective channel data by distributing them to the multicarrier. Forexample, when three carriers are used and a rate ⅓ encoder is used, themulticarrier scheme encodes the respective input data bit into threeencoded bits (i.e., symbols) using the rate ⅓ encoder and transmits theencoded bits using the three carriers after repetition and interleaving.This is well disclosed in Korean patent application No. 61616/1997 filedby the applicant of this invention. Here, the respective carriers eachhave a bandwidth of 1.2288 Mhz (hereinafter, referred to as 1.25 Mhz)which is identical to the IS-95 channel bandwidth. Therefore, the threecarriers have a combined or collective bandwidth of 3.6864 Mhz, which isidentical to three separate channel bandwidths.

[0013] The forward link of the 3G multicarrier system can employ anoverlay method where it shares the same frequency band with the IS-95forward channel. In this case, it may be interfered with the IS-95system. In addition, it is preferable to use the coding rate lower thanthe present coding rate of ⅓, even when the channel SNR is reduced dueto the bad channel environment or the increased distance between themobile station and the base station.

SUMMARY OF THE INVENTION

[0014] It is therefore an object of the present invention to providemethods and an apparatus for adaptively changing a coding rate ofchannel data according to the channel environment in a CDMAcommunication system.

[0015] It is another object of the present invention to provide atraffic channel transmission apparatus for a CDMA communication systemhaving a plurality of coding rates and orthogonal codes, whichdetermines a present channel condition and adaptively selects a codingrate and an orthogonal code according to the determination, and a methodfor operating the same.

[0016] It is further another object of the present invention to providea traffic channel transmission apparatus for a CDMA communication systemhaving a plurality of coding rates and orthogonal codes, which selectsthe coding rate and the orthogonal code according to control informationtransmitted from a transmission device, and a method for operating thesame.

[0017] It is still another object of the present invention to provide atraffic channel transmission apparatus for a multicarrier CDMAcommunication system having a plurality of coding rates and orthogonalcodes, which determines a present channel condition and adaptivelyselects the coding rate and the orthogonal code according to thedetermination, and a method for operating the same.

[0018] It is yet another object of the present invention to provide atraffic channel transmission device for a multicarrier CDMAcommunication system having a plurality of coding rates and orthogonalcodes, which selects the coding rate and the orthogonal code accordingto control information transmitted from a transmission device, and amethod for operating the same.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and other objects, features and advantages of thepresent invention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich like reference numerals indicate like parts. In the drawings:

[0020]FIG. 1 is a diagram illustrating a channel transmission device ina conventional CDMA communication system;

[0021]FIG. 2 is a diagram illustrating a decision apparatus for changinga channel data rate according to a channel environment according to anembodiment of the present invention;

[0022]FIG. 3 is a diagram illustrating a single carrier forward trafficchannel transmission device including plural encoders of differentrates;

[0023]FIG. 4 is a diagram illustrating a reverse traffic channelreception device including plural decoders of different rates;

[0024]FIG. 5 is a flowchart illustrating a method whereby a mobilestation, in response to a base station order, selects and encoder usinga paging channel and an access channel during a call setup according toan embodiment of the present invention;

[0025]FIG. 6 is a flowchart illustrating a method whereby a mobilestation, in response to a base station order, changes the rate duringthe call progressing according to an embodiment of the presentinvention;

[0026]FIG. 7A is a flowchart illustrating a method whereby a basestation changes a data channel rate upon reception of a rate changerequest message from a mobile station according to an embodiment of thepresent invention;

[0027]FIG. 7B is a flowchart illustrating a method whereby a basestation changes the data channel rate of a mobile station when a ratechange request message is not received from the mobile station accordingto an embodiment of the present invention;

[0028]FIG. 8 is a flowchart illustrating a procedure in which the mobilestation changes the rate upon reception of a rate change request messagefrom the base station and analyzes a channel environment to send a ratechange request message to the base station based on the analysisaccording to an embodiment of the present invention;

[0029]FIG. 9 is a flowchart illustrating a procedure in which the basestation changes an orthogonal code during a data channel rate changeaccording to an embodiment of the present invention; and

[0030]FIG. 10 is a diagram illustrating a multicarrier forward trafficchannel transmission device including a plurality of encoders havingdifferent rates and adaptively selects the encoders according to thechannel environment in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0031] A traffic channel transmission/reception device according to anembodiment of the present invention increases channel performance bydecreasing the coding rate thereby causing an increase in the codinggain. The method has particular applicability for those situations wherepath loss or interference increases between a base station and a mobilestation on a CDMA link channel. For example, when using a ⅙ coding raterather than a conventional ⅓ coding rate, it is possible to improveperformance against an increase in signal path loss, noise andinterference. Therefore, in a relatively bad channel environment, it ismore efficient to use the lower coding rate of ⅙ rather than the highercoding rate of ⅓.

[0032] An illustrative embodiment will be described which includes amethod of improving a receiver's performance by channel encoding at twodifferent rates as applied to a 3G multicarrier CDMA system.

[0033] In a CDMA communication system, under certain channel conditionsthe use of an encoder operated at a lower coding rate has the effect ofincreasing the channel gain and thereby improving channel performance.In the light of this, a system having a coding rate which is initiallyset for a call, adaptively selects the lower coding rate for the forwardchannel transmission to improve the performance. In the illustrativeembodiment, the channel transmission device comprises a plurality ofchannel encoders having different coding rates and correspondingorthogonal modulators for generating orthogonal codes. The channeltransmission device can adaptively control the coding rate and theorthogonal modulation according to the channel environment. Further, thechannel reception device examines the coding rate and the orthogonalcode according to control information output from the channeltransmission device and thereafter, performs orthogonal demodulation andchannel decoding for the received signal in accordance with the controlinformation.

[0034] Although the present invention will be described as comprisingtwo coding rates (i.e. ⅓ and ⅙), they are provided merely by way ofexample. It is to be appreciated that the use of other coding rates arewell within the scope of the present invention. Moreover, for purposesof illustration, the traffic channel of the forward link may becharacterized as comprising a base station as the transmission deviceand a mobile station as the reception device.

[0035]FIG. 2 is a block diagram of a decision apparatus for analyzing achannel environment and selecting a coding rate in response inaccordance with one aspect of the present invention.

[0036] Referring to FIG. 2, receiver part 211 processes a signalreceived from a sending station (i.e. base or mobile). The receiver 211extracts a power control bit (PCB) from the received signal to detect areceived signal strength indicator (RSSI), and outputs PCB, RSSI, andINFO data to a decision block 213.

[0037] The control block 213 analyzes the INFO, the PCB and the receivedsignal strength output from the receiver 211 and, if rate change isrequired, generates a control signal Csel for selecting a coding rate,orthogonal code number and length signals Output signals Wno and Wlengthare output from the decision block for selecting the orthogonal codecorresponding to the selected coding rate. The decision block 213compares a signal gain, the number of power increase requests minus thenumber of power decrease requests (i.e., the number of up command PCB'sminus the number of down command PCBs) and the energy of the receivedsignal strength with the respective threshold values to detect thechannel environment. That is, the decision block 213 generates thesignals Csel, Wno and Wlength for selecting the lower FEC rate, when theinput parameters have values lower than the lower bound thresholdvalues. That is when:

the signal gain<S_low_Th<P_high_Th, and (average E[RSSI])<R_low_Th

[0038] where

[0039] S_low_Th: is a PCB value accumulated for a particular duration;Th: represents the threshold value;

[0040] S_low, P_high, R_low: represent lower bound threshold values ofthe signal, the PCB and the RSSI, respectively).

[0041] Further, the decision block 213 generates the signals Csel, Wnoand Wlength for selecting the higher FEC rate, when the input parametershave values higher than the upper bound threshold values. That is when:

signal gain>S_high_Th>P_low_Th, and E[RSSI]>R_high_Th

[0042] where S_high_Th: is a PCB value accumulated for a particularduration;

[0043] In determining a channel data rate change the decision block 213can use all or some of the parameters.

[0044] A transmitter 215 transmits messages MSG, including a messagerequired for the rate change, output from the decision block 213 to thereceiver station. The apparatus described at FIG. 2 can be implementedeither at a BS or MS for sending the message MSG.

[0045]FIG. 3 is a block diagram illustrating a structure of a forwardlink traffic channel transmission device including a rate ⅓ encoder anda rate ⅙ encoder according to an embodiment of the present invention.

[0046] Referring to FIG. 3, a selector 301 has a first output connectedto an input of a first encoder 311 and a second output connected to aninput of a second encoder 312. The selector 301 receives input data tobe transmitted and selectively outputs the input data to the firstencoder 311 or the second encoder 312 according to the select signalCsel output from the decision block 213.

[0047] The first encoder 311, upon reception of data input from theselector 301, encodes the input data into data symbols at a first codingrate (the ⅓ coding rate). That is, the first encoder 311 encodes oneinput data bit into three symbols. A convolutional encoder or a turboencoder can be used for the first encoder 311. A first symbol repetitionpart 321 receives the data encoded at the first coding rate, and repeatsthe symbols output from the first encoder 311 as necessary so as tomatch the symbol rates of the data having different bit rates. A firstinterleaver 331 interleaves first encoded data output from the firstsymbol repetition part 321. A block interleaver can be used for thefirst interleaver 331.

[0048] The second encoder 312, upon reception of the data input from theselector 301, encodes and punctures the input data into data symbols ata second coding rate (the ⅙ coding rate). That is, the second encoder312 encodes one input data bit into six symbols. A convolutional encoderor a turbo encoder can be used for the second encoder 312. A secondsymbol repetition part 322 receives the data encoded at the secondcoding rate, and repeats the symbols output from the second encoder 312so as to match the symbol rates of the data having different bit rates.A second interleaver 332 interleaves second encoded data output from thesecond symbol repetition part 322. A block interleaver can be used forthe second interleaver 332.

[0049] A long code generator 391 generates long codes for the useridentification, which are uniquely assigned to the respectivesubscribers. A decimator 392 decimates the long codes so as to match arate of the long codes to a rate of the symbols output from theinterleavers 331 and 332. A selector 393 selectively outputs thedecimated long code output from the decimator 392 to a mixer 341 or amixer 342 according to the select signal Csel. The selector 393 switchesthe decimated long code to the first mixer 341 to select the ⅓ codingrate and to the second mixer 342 to select the 1/6 coding rate. Themixer 341 mixes the first encoded data output from the first interleaver331 with the long code output from the selector 393. The second mixer342 mixes the second encoded data output from the second interleaver 332with the long code output from the selector 393.

[0050] A first signal mapping part 351 converts levels of the binarydata output from the first mixer 341 by converting data “0” to “+1” anddata “1” to “−1”. A first orthogonal modulator 361 includes a firstorthogonal code generator (not shown) which generates a first orthogonalcode for orthogonally modulating the first encoded data according to theorthogonal code number and length signals Wno and Wlength output fromthe decision block 213. The first orthogonal modulator 361 multiples thefirst orthogonal code generated according to the orthogonal code numberand length signals Wno and Wlength by the data output from the firstsignal mapping part 351 to generate a first orthogonal modulationsignal. Here, it is assumed that the Walsh code is used for theorthogonal code and a Walsh code of length 256 is used for the dataencoded at the first coding rate of ⅓.

[0051] A second signal mapping part 352 converts levels of the binarydata output from the second mixer 342 by converting data “0” to “+1” anddata “1” to “−1”. A second orthogonal modulator 362 includes a secondorthogonal code generator (not shown) which generates a secondorthogonal code for orthogonally modulating the second encoded dataaccording to the orthogonal code number and length signals Wno andWlength output from the decision block 213. The second orthogonalmodulator 362 multiples the second orthogonal code generated accordingto the orthogonal code number and length signals Wno and Wlength by thedata output from the second signal mapping part 352 to generate a secondorthogonal modulation signal. Here, it is assumed that the Walsh code isused for the orthogonal code and a Walsh code of length 128 is used forthe data encoded at the second coding rate of ⅙.

[0052] A spreader 370 combines the first and second orthogonalmodulation signals output from the first and second orthogonalmodulators 361 and 362 with the received spreading sequence to spread atransmission signal. Here, the PN sequence can be used for the spreadingsequence and the QPSK spreader can be used for the spreader 370. A gaincontroller 380 controls a gain of the spread signal input from thespreader 370 according to a gain control signal Gc.

[0053] The operation of the traffic channel transmission device will beprovided with specific reference to FIGS. 2 and 3.

[0054] The decision block 213 analyzes the parameters PCB, receivedsignal strength (RSSI) and INFO output from the receiver 211 todetermine whether to change the channel data rate. Here, the parametersinclude the received signal strength RSSI, the accumulated value of thePCB received during a particular duration, some integer multiple of 1.25milliseconds, and the message indicator, INFO representing a request bythe other party for a change in the channel data rate duringcommunication. First, the transmitter 215 determines whether the signalstrength (i.e RSSI) of the signal received during communication is lowerthan the lower bound threshold value. When the strength RSSI of thereceived signal is lower than the threshold value, the current radiosensitivity is poor. In this case, the decision block 213 may generatethe signals Csel, Wno and Wlength to decrease the present channel datarate.

[0055] In addition, the mobile station examines the signals transmittedfrom the base station and outputs the power control bit PCB to controlthe transmission power of the base station through the reverse link, andvice versa through the forward link. The base station then examines thepower control bit PCB from the mobile station and counts the number ofpower-up PCBs and the number of the power-down PCBs received. When thecount value of the power-up PCBs, within a predetermined time durationexceeds a predetermined value, the decision block 213 may generate thecontrol signals to increase the current channel data rate. Otherwise, ifthe count value of the power-down PCBs, within a predetermined timeduration exceeds a predetermined value, the decision block 213 maygenerate the control signals to decrease the present channel data rate.

[0056] In addition, the rate change request can also be made at themobile station. In this case, the mobile station makes a request usingthe message INFO, and the decision block 213 in the base station thenreceives the request message INFO through the receiver 211.

[0057] The decision block 213 can use other parameters in addition or insubstitution of the parameters stated above to measure the channelenvironment and performance. The present illustrative embodiment,however, uses only the three parameters stated above. Furthermore,depending on the design of the algorithm of the decision block 213, itis also possible to initially change the channel data rate whenever therespective parameters are received or only when a subset of parametersare received. In addition, when the channel environment becomes poor,the decision block 213 can improve the channel environment by selectingthe lower coding rate. When the channel environment improves, thedecision block 213 can restore the coding rate to the original highercoding rate.

[0058] To change the coding rate the decision block 213 generates a neworthogonal code number and length signals Wno and Wlength to allocate anew channel during the coding rate change. When the coding rate ischanged, the orthogonal code should be also changed. To change thecoding rate the decision block 213 generates the select signal Csel forselecting the encoder having the corresponding coding rate, and theorthogonal code number and length signals Wno and Wlength for generatinga new orthogonal code corresponding to the selected coding rate. Whenthe encoder having a lower coding rate is selected, a shorter orthogonalcode should be generated; when the encoder having a higher coding rateis selected, a longer orthogonal code should be generated.

[0059]FIG. 3 shows the transmission channel structure in which theforward link is switched to the first encoder 311 of the ⅓ FEC rate orthe second encoder 312 of the ⅙ FEC rate in accordance with the channelenvironment. The data input path is switched to either the encoder 311or the encoder 312 by the selector 301. Thus, the transmission dataundergoes a different FEC rate according to the selected data path. Thatis, based on the select signal Csel output from the decision block 213,the selector 301 switches the input data to the first encoder 311 whenthe channel environment is good, and switches the input data to thesecond encoder 312 when channel environment is poor.

[0060] In addition, since the orthogonal code should be also changedaccording to the change of the FEC rate, it is necessary to select oneof the orthogonal modulators 361 and 362 according to the change of theFEC rate. That is, when the first encoder 311 is selected to use the ⅓FEC rate, the orthogonal code generator in the first orthogonalmodulator 361 generates the orthogonal code of length 256 according tothe orthogonal code number and length Wno and Wlength. Therefore, theorthogonal modulator 361 multiplies the signal encoded at the ⅓ FEC rateby the orthogonal code to generate the first orthogonal modulationsignal, and the spreader 370 spreads the first orthogonal modulationsignal using the PN sequences PNI and PNQ.

[0061] Furthermore, when the second encoder 312 is selected to use the ⅙FEC rate, the orthogonal code generator in the second orthogonalmodulator 362 generates the orthogonal code of length 128 according tothe orthogonal code number and length Wno and Wlength. Therefore, theorthogonal modulator 362 multiplies the signal encoded at the ⅙ FEC rateby the orthogonal code to generate the second orthogonal modulationsignal, and the spreader 370 spreads the second orthogonal modulationsignal using the PN sequences PNI and PNQ.

[0062] As can be appreciated from the foregoing description, there is nochange in structure of the spreader 370 for spreading the orthogonalmodulation signal using the PN sequences. Accordingly, the ⅙ FEC ratescheme is identical in structure to the ⅓ FEC rate scheme, except forthe encoder and interleaver. In particular, in the ⅙ FEC rate scheme,the bit rate of the final stage is increased from 576 to 1152 bits perframe. In addition, the interleaver size is also increased to twice itsnormal size.

[0063]FIG. 4 illustrates the structure of a reception device accordingto an embodiment of the present invention. The reception device iscontrolled by a decision block 213 having the same structure as thatshown in FIG. 2. In the figure, a despreader 410 despreads a receivedsignal by combining the received signal with the spreading (i.e. PN)sequences. A selector 420 has a first output connected to a firstorthogonal demodulator 431 and a second output connected to a secondorthogonal demodulator 432. The selector 420 switches the despreadsignal output from the despreader 410 to the first orthogonaldemodulator 431 or the second orthogonal demodulator 432 according to aselect signal Csel output from the decision block 213.

[0064] The first orthogonal demodulator 431 includes a first orthogonalcode generator for generating a first orthogonal code according to theorthogonal code number and length signals Wno and Wlength, output fromthe decision block 213. When connected to the selector 420, the firstorthogonal demodulator 431 generates the first orthogonal code accordingto the orthogonal code number and length signals Wno and Wlength andmultiplies the despread data by the first orthogonal code to output afirst orthogonal demodulation signal. Here, it is assumed that a Walshcode is used for the orthogonal code and a Walsh code of length 256 isused for the data encoded at the ⅓ coding rate. A first signal demappingpart 441 demaps the 4-level signal output from the first orthogonaldemodulator 431 into binary data by converting data “+1” to “0” and data“−1” to “1”.

[0065] The second orthogonal demodulator 432 includes a secondorthogonal code generator for generating a second orthogonal codeaccording to the orthogonal code number and length signals Wno andWlength output from the decision block 213. When connected to theselector 420, the second orthogonal demodulator 432 generates the secondorthogonal code according to the orthogonal code number and lengthsignals Wno and Wlength and multiplies the despread data by the secondorthogonal code to output a second orthogonal demodulation signal. Here,it is assumed that a Walsh code is used for the orthogonal code and aWalsh code of length 128 is used for the data encoded at the ⅙ codingrate. A second signal demapping part 442 demaps the 4-level signaloutput from the second orthogonal demodulator 432 into binary data byconverting data “+1” to “0” and data “−1” to “1”.

[0066] A long code generator 491 generates a long code identical to thatgenerated at the transmitter. Here, the long codes are the useridentification codes, and the different long codes are assigned to therespective subscribers. A decimator 492 decimates the long code so as tomatch a rate of the long code to a rate of the signals output from thesignal demapping parts 441 and 442. A selector 493 switches thedecimated long code output from the decimator 492 to a mixer 451 or amixer 452 according to the select signal Csel. In other words, theselector 493 switches the decimated long code to the first mixer 451 toselect the ⅓ coding rate, and switches the decimated long code to thesecond mixer 452 to select the ⅙ coding rate. The first mixer 451 mixesan output of the signal demapping part 441 with the long code to deletethe long code contained in the received signal, and the second mixer 452mixes an output of the signal demapping part 442 with the long code todelete the long code contained in the received signal.

[0067] A first deinterleaver 461 deinterleaves the received signaloutput from the first mixer 451 to rearrange the interleaved firstencoded data into the original state. A first symbol extraction part 471extracts the original encoded data by deleting the symbol-repeatedencoded data from the output of the first deinterleaver 461. A firstdecoder 481 having a ⅓ decoding rate, decodes the encoded data outputfrom the first symbol extraction part 471 into the original data.

[0068] A second deinterleaver 462 deinterleaves the received signaloutput from the second mixer 452 to rearrange the interleaved secondencoded data into the original state. A second symbol extraction part472 extracts the original encoded data by deleting the symbol-repeatedencoded data from the output of the second deinterleaver 462. A seconddecoder 482 having a ⅙ decoding rate, decodes the encoded data outputfrom the second symbol extraction part 472 into the original data.

[0069] It should be appreciated from FIG. 4 that the reception device ofthe CDMA communication system has a construction which is the inverse ofthat shown in FIG. 3.

[0070] As described above, the illustrative embodiment discloses amethod of using the ⅙ FEC rate for the communication between basestation and mobile station within a bad channel environment which hasbeen degraded due to either a decrease of SNR or an increased BER inorder to provide better link performance as compared with the case wherethe ⅓ FEC rate is used. In operation, a base station uses both the ⅓ FECrate and the ⅙ FEC rate. In the case where only the ⅓ FEC rate is used,there are 256 available orthogonal codes of length 256. When only the ⅙.FEC rate is used there are 128 available orthogonal codes of length 128.However, when the two orthogonal code sets are both used, the use of asingle orthogonal code of length 128 makes two of the correspondingorthogonal codes of length 256 unavailable. The use of one orthogonalcode of length 256 makes one orthogonal code of length 128 unavailable.This is because there are orthogonal codes that are correlated betweenthe two orthogonal code sets.

[0071] When all of the users have a ⅓ rate FEC, the maximum number ofusers can be 256, however the maximum number of users will be 128 if allthe users have a ⅙ FEC rate. For this reason, use of the selectable ⅙FEC rate is restricted since it decreases the system capacity (i.e., thenumber of users). It is possible to limit the number of forward channelsusing the ⅙ FEC rate by allowing use of the ⅙ rate encoder to theforward link hating a high signal path loss, a high signal transmissionpower or a high BER. In addition, since use of one orthogonal code oflength 128 precludes the use of two orthogonal codes of length 256, thenumber of link channels using the rate ⅙ encoder is limited as long asit is possible to assign a sufficient number of orthogonal codes themobile stations. When utilizing the method of present invention the basestation should be designed to switchably use both the rate ⅓ encoder andthe rate ⅙ encoder. The base station could order a mobile station in acertain condition to switch from the ⅓ FEC rate to the ⅙ FEC rate, andcould order another mobile station in a certain other condition,described below, to switch from the ⅙ FEC rate to the ⅓ FEC rate.

[0072] Moreover, in some cases, it is also possible to initially selectone of the ⅓ FEC rate and the ⅙ FEC rate at the beginning of a channelsetup process. Also, the base station may allow a mobile stationrequesting the high forward traffic channel transmission power topreferentially use the ⅙ FEC rate as long as available orthogonal codescan be assigned without establishing the conditions required todetermine whether to permit a rate change to either the ⅓ FEC rate orthe ⅙ FEC rate. Other possible setting conditions (i.e., energy perchip: Ec, or chip energy to interference ratio: Ec/Io) can be determineddepending on the received power of the forward pilot channel, and thesignal path loss, fading and signal transmission power of the forwardlink or the reverse link.

[0073] Orthogonal Code Assignment

[0074] The following is a description and explanation of the presentinvention directed with specific reference to orthogonal codeassignment. Since the orthogonal codes are generated through theHadamard transform, there exist non-orthogonal codes between a 2N*2Northogonal code set and a 2(N+1)*2(N+1) orthogonal code set. Therefore,for a base station allowing 2 sets of different orthogonal codes (e.g.,an orthogonal code set of length 2*N and 2*(N+1)), orthogonal codesamong the 2N*2N orthogonal code set to a forward channel, carefulselection is necessary in order to maintain the orthogonality with theexisting assigned orthogonal code of length 2(N+1). This means that thebase station should examine the non-orthogonality between everyorthogonal code of length 2N for a new assignment and all the existingassigned orthogonal codes of length 2(N+1).

[0075] The structure shown in FIGS. 2 through 4 can be so designed as tochange the FEC rate at the forward link.

[0076]FIGS. 5 and 6 illustrate a method for switching the coding rate tothe ⅓ FEC rate or the ⅙ FEC rate for the forward link of a 3G CDMAsystem.

[0077]FIG. 5 illustrates a method in which the base station allows themobile station to request the second encoder 312 of the ⅙ FEC ratethrough the paging and access channels during the call setup. Adescription will be provided below directed to the operation ofselecting the ⅙ FEC rate for the forward link from the start of the callthrough the access channel and the paging channel at the call setupstage,

[0078]FIG. 6 illustrates a method in which the base station allows themobile station to change the coding rate in the middle of a call. Adescription will be provided below directed to an operation of switchingfrom the ⅓ FEC rate to the ⅙ FEC rate during the call processing in theIS-95B system.

[0079] Referring to FIG. 5, for the call setup, the mobile station sendsan origination message (shown in the Table 1) to the base station 511.In the origination message of Table 1, a new MOB_P_REV value (which isdifferent from the existing value) is assigned to the mobile stationwhich can change the coding rate, and the mobile station sends theorigination message by putting its own MOB_P_REV value therein.Thereafter, upon reception of the origination message, the base stationsends to the mobile station a channel assignment message 515 (shown inthe following Tables 2A to 2G).

[0080] Table 2B shows the channel assignment message forASSIGN_MODE=“000”,

[0081] Table 2C shows the channel assignment message forASSIGN_MODE=“001”,

[0082] Table 2D shows the channel assignment message forASSIGN_MODE=“010”,

[0083] Table 2E shows the channel assignment message forASSIGN_MODE=“011”,

[0084] Table 2F shows the channel assignment message forASSIGN_MODE=“100”,

[0085] Table 2G shows the channel assignment message forASSIGN_MODE=“101”.

[0086] In step 513, the base station may first send a BS_ACK_Order inacknowledgment of the origination message. In the channel assignmentmessage, a new ENCODER_RATE field is assigned for the coding rate tosend the designated coding rate. The mobile station then fixes thecoding rate according to the received channel assignment message andsearches the forward link channel using the given frequency band andorthogonal code. TABLE 1 Field Length [bits] MSG_TYPE (“00000100”) 8ACK_SEQ 3 MSG_SEQ 3 ACK_REQ 1 VALID_ACK 1 ACK_TYPE 3 MSID_TYPE 3MSID_LEN 4 MSID 8 × MSID_LEN AUTH_MODE 2 AUTHR 0 or 18 RANDC 0 or 8COUNT 0 or 6 MOB_TERM 1 SLOT_CYCLE_INDEX 3 MOB_P_REV 8 SCM 8REQUEST_MODE 3 SPECIAL_SERVICE 1 SERVICE_OPTION 0 or 16 PM 1 DIGIT_MODE1 NUMBER_TYPE 0 or 3 NUMBER_PLAN 0 or 4

[0087] TABLE 2A Field Length [bits] MSG_TYPE (“00001000”) 8 One or moreoccurrences of the following record: ACK_SEQ 3 MSG_SEQ 3 ACK_REQ 1VALID_ACK 1 ADDR_TYPE 3 ADDR_LEN 4 ADDRESS 8 × ADDR_LEN ASSIGN_MODE 3ADD_RECORD_LEN 3 Additional Record Fields 8 × ADD_RECORD_LENENCODER_RATE 2 RESERVED 0-5 (as needed)

[0088] TABLE 2B if ASSIGN_MODE = “000”, the additional record fieldsshall be: Field Length [bits] FREQ_INCL 1 CODE_CHAN 8 CDMA_FREQ 0 or 11FRAME_OFFSET 4 ENCRYPT_MODE 2 RESERVED 0-7 (as needed)

[0089] TABLE 2C if ASSIGN_MODE = “001”, the additional record fieldsshall be: Field Length [bits] RESPOND 1 FREQ_INCL 1 CDMA_FREQ 0 or 11One or more occurrences of the following field: PILOT_PN 9 RESERVED 0-7(as needed)

[0090] TABLE 2D if ASSIGN_MODE = “010”, the additional record fieldsshall be: Field Length [bits] RESPOND 1 ANALOG_SYS 1 USE_ANALOG_SYS 1RESERVED 5 BAND_CLASS 5

[0091] TABLE 2E if ASSIGN_MODE = “011”, the additional record fieldsshall be: Field Length [bits] SID 15  VMAC 3 ANALOG_CHAN 11  SCC 2 MEM 1AN_CHAN_TYPE 2 DSCC_MSB 1 RESERVED 5 BAND_CLASS 5

[0092] TABLE 2F if ASSIGN_MODE = “100”, the additional record fieldsshall be: Field Length [bits] FREQ_INCL 1 RESERVED 74 DEFAULT_CONFIG 3GRANTED_MODE 2 CODE_CHAN 8 FRAME_OFFSET 4 ENCRYPT_MODE 2 BAND_CLASS 0 or5 CDMA_FREQ 0 or 11

[0093] TABLE 2G if ASSIGN_MODE = “101”, the additional record fieldsshall be: Field Length [bits] RESPOND 1 FREQ_INCL 1 BAND_CLASS 0 or 5CDMA_FREQ 0 or 11 One or more occurrences of the following field:PILOT_PN 9 RESERVED 0-7 (as needed)

[0094] Referring to FIG. 6, during an active state where a call isconnected between the base station and the mobile station, the basestation examines the channel environment with the mobile station byestimating, for example, the RSSI. In step 611, the base stationestimates the RSSI, selects a coding rate lower than the present codingrate when the RSSI is lower than a threshold value R_low_th, and selectsa coding rate higher than the present coding rate when the RSSI ishigher than a threshold value R_high_th.

[0095] In the active state, since the base station and the mobilestation exchange messages through the traffic channels, a new field forthe encoder rate and the orthogonal code is added to a serviceconfiguration shown in the following Table 3 in order to switch thecoding rate of the mobile station. 16 bits are assigned for the newfield of the service configuration; the first 2 bits are assigned forthe encoder rate, the next 8 bits are assigned for the orthogonal code,and the last 6 bits are reserved bits. Although a RECORD_LEN value of aservice request message shown in the following Table 4 is 12 in theexisting IS-95B Standard, it is 14 in the present embodiment since twooctets are added. This is changed in the same manner even in a serviceresponse message shown in Table 5 and a service connect message shown inTable 6. The contents of the service configuration are input to thetype-specific fields of the messages (i.e., the service request message,the service response message and the service connect message).

[0096] By way of example, Table 3 represents the service configurationfor the case where the two coding rates of ⅓ and ⅙ are used. In thisexample, if the mobile station includes at least two encoders havingdifferent coding rates and the orthogonal code length is changedaccording to the coding rates, the lengths of the ENCODER_RATE field andthe CODE_CHAN field of Table 3 are also changed to accomodate all thecases, and the RECORD_LEN values of Tables 4, 5 and 6 are also adjusted.

[0097] After the service configuration is corrected, the base stationsends the service request message and selects the new coding rate andorthogonal code to change the coding rate, in step 613. In response tothe service request message, the mobile station then outputs the serviceresponse message through the reverse traffic channel, in step 615. Here,if the mobile station does not respond to the service request message,the base station repeats step 613 by continually re-sending the servicerequest message to change the coding rate until the mobile station sendsthe service response message responding to the request message. In step617, if the service configuration of the mobile station coincides withthat of the base station, the base station sends the service connectmessage and sets a rate change action time of the ACTION_TIME field, orimplements the service comment message by default a predetermined timeafter receiving the message. In step 619, the mobile station sends aservice connect completion message through the reverse link toacknowledge the service connect message. In step 621, the mobile stationand the base station both change the rate at the set action time. TABLE3 Type-Specific Field Length [bits] FOR_MUX_OPTION 16 REV_MUX_OPTION 16FOR_RATES 8 REV_RATES 8 NUM_CON_REC 8 NUM_CON_REC occurrences of thefollowing record: RECORD_LEN 8 CON_REF 8 SERVICE_OPTION 16 FOR_TRAFFIC 4REV_TRAFFIC 4 ENCODER_RATE 2 CODE_CHAN 8 RESERVED 6

[0098] TABLE 4 Field Length [bits] MSG_TYPE (“00010010”) 8 ACK_SEQ 3MSG_SEQ 3 ACK_REQ 1 ENCRYPTION 2 SERV_REQ_SEQ 3 REQ_PURPOSE 4 Zero orone occurrence of the following record: RECORD_TYPE 8 RECORD_LEN 8Type-specific fields 8 × RECORD_LEN

[0099] TABLE 5 Field Length [bits] MSG_TYPE (“00010011”) 8 ACK_SEQ 3MSG_SEQ 3 ACK_REQ 1 ENCRYPTION 2 SERV_REQ_SEQ 3 RESP_PURPOSE 4 Zero orone occurrence of the following record: RECORD_TYPE 8 RECORD_LEN 8Type-specific fields 8 × RECORD_LEN

[0100] TABLE 6 Field Length [bits] MSG_TYPE (“00010100”) 8 ACK_SEQ 3MSG_SEQ 3 ACK_REQ 1 ENCRYPTION 2 USE_TIME 1 ACTION_TIME 6 SERV_CON_SEQ 3RESERVED 5 One occurrence of the following record: RECORD_TYPE 8RECORD_LEN 8 Type-specific fields 8 × RECORD_LEN

[0101] TABLE 7 Field Length [bits] MSG_TYPE (“00010100”) 8 ACK_SEQ 3MSG_SEQ 3 ACK_REQ 1 ENCRYPTION 2 SERV_REQ_SEQ 4 RESERVED 3

[0102] It is possible to change the coding rate of the voice service andthe packet data service differently. That is, during the packet dataservice, the coding rate of the supplemental channel for the packetservice can be processed through a dedicated control channel (DCCH). Inaddition, when the message is received through the traffic channel, notthrough the DCCH, the coding rate can be processed in the same mannerrequired by the fundamental channel. For example, when 2 bits are usedfor the coding rate (providing four available cases), the two cases areused in changing the coding rate for the fundamental channel and othertwo cases are used in changing the coding rate for the supplementalchannel.

[0103] As used in the examples above, 256 orthogonal codes of length 256bits are used for the ⅓ coding rate and 128 orthogonal codes of length128 bits are used for the ⅙ coding rate. Here, since the orthogonalcodes of length 256 are created by applying the Hadamard transform tothe orthogonal codes of length 128, one orthogonal code of length 128does not satisfy orthogonality with two orthogonal codes of length 256,losing the orthogonality between the channels. Therefore, assignment ofone orthogonal code of length 128 decreases the available number oforthogonal codes of length 256 by two. Alternately, assignment of oneorthogonal code of length 256 makes one orthogonal code of length 128unusable. The base station continuously monitors the assigned orthogonalcodes of length 128 and 256 to assign the new orthogonal codes so as toavoid the non-orthogonality with the previously assigned orthogonalcodes.

[0104] In this manner, the present embodiment maintains a good channelcondition by changing the coding rate and the orthogonal code accordingto the channel environment. Here, the transmission power is consideredto maintain a better tolerance for the channel environment. Further, theorthogonal code is so assigned to avoid breaking the orthogonality amongthe forward link channels. This is, it is desirable to have lowertransmission power for the same channel performance. Accordingly, thepresent embodiment changes the coding rate according to the channelenvironment, taking into consideration the transmission power. Further,if the orthogonal code is changed while the coding rate is changed bythe base station or the mobile station in the same cell, it isdetermined whether there is an orthogonal code causing thenon-orthogonality between the different orthogonal code sets. In thisway, it is possible to solve the interference and non-orthogonalityproblems of the CDMA communication system.

[0105]FIGS. 7A and 7B are flowcharts illustrating a rate changeoperation performed in the decision block 213 of the base station. Morespecifically, FIG. 7A illustrates a rate change operation performed inthe base station upon reception of the rate change request message froma particular mobile station, and FIG. 7B illustrates the procedure wherethe base station analyzes the channel environment of the mobile stationto determine whether to change the rate when the mobile station does notgenerate the rate change request message. It should be noted that thebase station can perform the procedures of FIGS. 7A and 7B in parallel.

[0106]FIG. 8 illustrates the procedure where the mobile station performsthe rate change operation with the base station, for the situation wherethe mobile receives a rate change request message from the base stationor when a rate change condition occurs as the channel environment ischanged.

[0107]FIG. 9 is a flowchart illustrating a procedure for assigning anorthogonal code corresponding to a change in the coding rate. That is,when assigning a forward channel to the mobile station, the base stationassigns orthogonal codes in such a manner that the number of availableorthogonal codes is as large as possible. FIG. 9 shows the procedure inwhich the base station assigns the orthogonal codes to the mobilestation according to an embodiment of the present invention.

[0108] The present embodiment assumes that coding rate and the length ofthe corresponding orthogonal codes are simultaneously changed inaccordance with the channel environment. However, it is also possible toindependently change the coding rate and the length of the orthogonalcode. Furthermore, the present embodiment assigns the longer orthogonalcode when the coding rate is increased (e.g., from ⅙ to ⅓), and assignsthe shorter orthogonal code when the coding rate is decreased (e.g.,from ⅓ to ⅙), thereby maintaining the same chip rate irrespective of thechange in the rate. However, it is also possible to change the codingrate and the orthogonal code without maintaining the same chip rateduring the channel communication between the base station and the mobilestation.

[0109] In the following description, the procedure for assigning theorthogonal code will be described with reference to FIG. 9, and then therate change procedure between the base station and the mobile stationwill be described with reference to FIGS. 7A, 7B and 8.

[0110] Referring initially to FIG. 9, when a mobile station requestsassignment of the orthogonal code of length N (where N=2^(K)) accordingto a change in the channel assignment or the coding rate, a ratecontroller (not shown) searches for the available orthogonal codes instep 911. Here, the orthogonal codes should be assigned such that theavailable orthogonal codes are maximized. To this end, in step 913, therate controller searches an orthogonal code table to determine whetherthere are unused orthogonal codes of length N. When all the orthogonalcodes of length N are used (i.e., assigned to the channel), theprocedure goes to step 929 to indicate unavailability of the orthogonalcodes and then terminates.

[0111] However, when there are available orthogonal codes of length N,the available orthogonal codes are written in a search list W(k), instep 915. The search list W(k) stores information about the unusedorthogonal codes in the form of w(k,i) as follows:${W(k)} = \begin{bmatrix}{w\left( {k,l_{1}} \right)} \\{w\left( {k,l_{2}} \right)} \\{w\left( {k,l_{3}} \right)} \\\vdots \\{w\left( {k,l_{N}} \right)}\end{bmatrix}$

[0112] where 0≦1₁<1₂<1₃ . . . N−1

[0113] where k is an integer representing the length of the Walsh codesand i is a Walsh code number, where i=0, 1, 2, . . . , N−1. Accordingly,if it is assumed that 11th, 12th, 15th, 21th and 30th orthogonal codesamong the orthogonal codes of length 2^(k) are not in use, the searchlist W(k) consists of the orthogonal codes w(k,11), w(k,12), w(k,15),w(k,21) and w(k,30).

[0114] After that, in step 917, a search procedure 1 is performed on thesearch list to search those orthogonal codes which are non-orthogonalwith orthogonal codes in use whose length is longer than 2^(k.), and toextract those orthogonal codes from the search list W(k). That is, inthe search procedure 1, the orthogonal codes not satisfying theorthogonality with the orthogonal codes presently in use among theorthogonal codes of length longer than 2^(k) are deleted from the searchlist W(k). Stated more precisely, the orthogonal codes that are notorthogonal with the orthogonal codes w(k+j,i) (where j≧1, i=0, 1, 2, . .. , 2^(k+1)−1), are deleted from the search list W(k). Variable j isincremented by one to increase the length of the orthogonal code. Thesearch and extraction procedure is repeated for all the orthogonal codesof length 2^(K+J) with all the orthogonal codes in the list W(k). Thesearch procedure 1 performed in step 917 is defined as:

[0115] SEARCH PROCEDURE 1

[0116] 1. set j←1

[0117] 2. while k+j≦maximum

[0118] do {

[0119] 2.1 find Walsh code(s) w(k,i) in the list W(k), which is (are)not orthogonal with w(k+j,i) in use can be equal to a subset of{i=0,1,2, . . . , 2^(k+j)−1}

[0120] 2.2 extract the Walsh codes w(k+i) which satisfy 2.1 from searchWalsh code list W(k)

[0121] 2.3 set j←j+1

[0122] }

[0123] After performing the search procedure 1, it is determined in step919 whether there are any remaining orthogonal codes in the search listW(k) (i.e. is w(k,i)>0). When the search list W(k) is empty, does nothave any orthogonal code, an indication of that state is provided instep 929.

[0124] However, when the search list W(k) is not empty, the processcontinues to step 921. At step 921, a search is made for the orthogonalcodes w(k,j) in the list W(k) to determine whether an orthogonal codew(k_(J)(J+N)/2 mod N is presently in use or not. If such orthogonalcodes exist in the search list W(k), the corresponding orthogonal codesare assigned as available orthogonal codes in step 927.

[0125] However, when the search list W(k) does not have thecorresponding orthogonal codes, a second search procedure 2 is performedin step 923 to delete the orthogonal codes not satisfying theorthogonality with the orthogonal codes presently in use among theorthogonal codes of length shorter than 2^(k). Stated more precisely,among the presently used orthogonal codes w(k−j,i) (where j≧1, i=0, 1,2, . . . , 2^(k−1)−1), those orthogonal codes not satisfying theorthogonality with the orthogonal codes stored in the search list W(k)are deleted from the search list W(k). As j is incrementally decreasedto decrease the length of the orthogonal code, the search and extractionprocedure is repeated for all the orthogonal codes. The search procedure2 performed in step 923 is defined as:

[0126] SEARCH PROCEDURE 2

[0127] 1. set j←1

[0128] 2. while k−j≧1

[0129] do {

[0130] 2.1 find Walsh code(s) w(k,i) in the list W(k), which is (are)not orthogonal with w(k−j,i) in use can be equal to a subset of{i=0,1,2, . . . , 2^(k−j)−1}

[0131] 2.2 extract the Walsh codes w(k+i) which satisfy 2.1 from searchWalsh code list W(k)

[0132] 2.3 set j←j+1

[0133] }

[0134] After performing the search procedure 2, it is determined in step925 whether there are any remaining orthogonal codes in the search listW(k) (i.e., is w(k,i)>0). When the search list W(k) is empty anindication is provided in step 929. However, when the list is not emptythose remaining orthogonal codes in the list W(k) are assigned as theavailable orthogonal codes in step 927.

[0135] The operation of assigning orthogonal codes will be summarized asfollows.

[0136] When the orthogonal code to be provided is of length N=2^(k), theunused orthogonal codes w(k,i) of length N are written in the searchlist W(k) in step 915. Here, i is an orthogonal code number Wno which isa Hadamard matrix element number.

[0137] As an example of the embodiment of a system having orthogonalityof length N=2^(K), k=4, 5, 6, it is assumed that the orthogonal code tobe provided is of length N=2^(K), k is 5, and there are three orthogonalcode lengths of k=4, k=5 and k=6. In addition, it is assumed that theorthogonal codes w(k,i) written in the search list W(k) are w(5,10),w(5,11), w(5,12), w(5,26), w(5,27) and w(5,28) of i=10, 11, 12,(10+2⁵/2)mod 2⁵=26, (11+2⁵/2)mod 2⁵=27 and (12+2⁵/2)mod 2⁵=28.Furthermore, for simplicity, such a pair of orthogonal codes w(5,10) andw(5,26), a pair of orthogonal codes w(5,11) and w(5,27) and a pair oforthogonal codes w(5,12) and w(5,28) are respectively referred to ashalf complement orthogonal codes with respect each other.

[0138] The orthogonal codes presently not in use or the orthogonal codesof interest are represented as follows: Here, the orthogonal codesw(6,28) and w(4,11) are in use.

[0139] That is, if we let

[0140] w(4,10)=B, w(4,11)=C and w(4,12)=D, then we can represent asfollows from the Hadamard transformation.

[0141] w(5,10)=BB, w(5,11)=CC, w(5,12)=DD, w(5,26)=B{overscore (B)},w(5,27)=C{overscore (C)}, w(5,28)=D{overscore (D)}, w(6,11)=CCCC,w(6,26)=B{overscore (B)}B{overscore (B)}, w(6,27)=C{overscore(C)}C{overscore (C)}, w(6,28)=D{overscore (D)}D{overscore (D)},w(6,43)=CC{overscore (CC)}, w(6,58)=B{overscore (BB)}B,w(6,59)=C{overscore (CC)}C and w(6,60)=D{overscore (DD)}D.

[0142] The barred codes represent complementary codes.

[0143] Combinations of the orthogonal codes are shown in the followingTable 8, in which it is assumed that the orthogonal codes w(6,28),w(5,10), w(5,12) and w(4,11) are in use. In Table 8, the orthogonalcodes of length k=5 have a relationship (half complement orthogonal codeto each other) to the search list W(k=5). Table 8 shows the orthogonalcodes, when the orthogonal code w(6,28) is in use and the orthogonalcode w(4,11) is not in use. Further, the underlined orthogonal codes inTable 8 are the orthogonal codes in the search list W(k). TABLE 8 k = 4k = 5 k = 6 w(6,11) = CCCC w(5,10) = BB w(6,26) = B{overscore(B)}B{overscore (B)} w(4,10) = B w(5,11) = CC w(6,27) = C{overscore(C)}C{overscore (C)} w(4,11) = C w(5,12) = DD w(6,28) = D{overscore(D)}D{overscore (D)} w(4,12) = D w(5,26) = B{overscore (B)} w(6,43) =CC{overscore (CC)} w(5,27) = C{overscore (C)} w(6,58) = B{overscore(BB)}B w(5,28) = D{overscore (D)} w(6,59) = C{overscore (CC)}C w(6,60) =D{overscore (DD)}D

[0144] Referring collectively to Table 8 and FIG. 9, in step 917, searchprocedure 1, a search is conducted of search list W(k) of orthogonalcodes w(5,11), w(5,26), w(5,27) and w(5,28) to determine which codes inthe list are not orthogonal with those orthogonal codes of length2^(k+1) presently in use. The codes in the list which do not satisfy theorthogonality test with codes of length 2^(k+1) are deleted from thesearch list W(k). As a result, in accordance with the search procedure1, orthogonal code w(5,28) does not satisfy the criteria in that it isnot orthogonal with orthogonal code w(6,28), presently in use.Therefore, code w(5,28) is deleted from the search list W(k).

[0145] Thus, after the search procedure 1 is performed, the search listcontains W(k)={w(5,11), w(5,26), w5,27)}. Since the search list is notempty, W(k)=3, the condition of step 919 (the number of W(k)>0) issatisfied. Further, since the half complement orthogonal code oforthogonal codes w(5,26) and w(5,(26+16)mod 32)=w(5,10) are already inuse, the condition of step 921 is also satisfied. Accordingly, theorthogonal code w(5,26) is assigned as an available orthogonal code.

[0146] If the orthogonal code w(5,10) is not in use then the elements ofthe search list W(k) after performing the search procedure 1 arew(5,10), w(5,11), w(5,26) and w(5,27), therefore the search list W(k)has no orthogonal code satisfying step 921. Then, the search procedure 2is performed in step 923. In the search procedure 2, for thoseorthogonal codes of length 2^(k−1) (i.e., k−1=4) in the search listW(k), those which are not orthogonal with the orthogonal codes presentlyin use are deleted from the search list W(k). Since the orthogonal codew(4,11)=C is in use, the orthogonal codes w(5,11)=CC andw(5,27)=C{overscore (C)} are deleted from the search list W(k). As aresult, the orthogonal codes stored in the search list W(k) areW(k=5)={w(5,10), w(5,26)}, which satisfies the condition of step 925.Thus, in step 927, the orthogonal codes w(5,10) and w(5,26) are assignedas the available orthogonal codes.

[0147] Assignment of the orthogonal codes is performed by the decisionblock 213 of FIG. 2. In assigning new orthogonal codes of length N, thedecision block 213 first determines whether there are availableorthogonal codes among the orthogonal codes of length N to be used. Whenthere are available orthogonal codes of length N, the decision block 213examines the available orthogonal codes to determine whether there areorthogonal codes not satisfying orthogonality with the orthogonal codesfor the forward channel assigned to the other existing forward links andavoids assigning those corresponding correlated codes, if any. Whenthere are available orthogonal codes available according to theprocedure of FIG. 9, the corresponding orthogonal code length and numberinformation is output to assign the orthogonal codes. Accordingly, in aCDMA communication system, when channel data is transmitted at avariable data rate, the base station can effectively assign orthogonalcodes to the mobile station such that the orthogonal codes assigned tothe different mobile stations and channels still maintain orthogonalitywith new orthogonal codes. Therefore, the communication systemsupporting the variable data rate can efficiently use the orthogonalcode resources and quickly assign the orthogonal codes.

[0148] The term “rate” used in connection with FIGS. 7A, 7B and 8 refersto the coding rate and/or the length of the orthogonal code. A “firstrate change condition” means a condition for switching from the higherrate to the lower rate, and a “second rate change condition” means acondition for switching from the lower rate to the higher rate. Forexample, the first rate change condition for changing the higher rate tothe lower rate means that the channel environment is changed from, forexample, a state where the ⅓ coding rate and the orthogonal code oflength 256 are used to a state where the ⅙ coding rate and theorthogonal code of length 128 are used. Likewise, the second rate changecondition for changing the lower rate to the higher rate means that thechannel environment is changed from, for example, a state where the ⅙coding rate and the orthogonal code of length 128 are used to a statewhere the ⅓ coding rate and the orthogonal code of length 256 are used.In the present embodiment, when the higher coding rate is used, thelonger orthogonal code is assigned, and when the lower coding rate isused, the shorter orthogonal code is assigned, to maintain a constantdata rate.

[0149] Referring to FIGS. 7A and 7B, the decision block 213 of the basestation analyzes the received signal in step 711, to determine whetherthe rate change request message is received from a mobile station. Whenthe rate change request message is received from the mobile station instep 711, the decision block 213 of the base station determines in step713 whether the received rate change request message represents a changeto the higher rate or to the lower rate.

[0150] If the received rate change request message represents a changeto the lower rate in step 713, the decision block 213 of the basestation examines, in step 715 whether the first rate change condition issatisfied. Here, the first rate change condition where the base stationdecreases the coding rate, represents the conditions shown in thefollowing Table 9. In the embodiment, it is assumed that the first ratechange condition is satisfied in the case where at least three, or two,conditions including condition 1 and condition 4 in Table 9 aresatisfied. TABLE 9 Condition Decision 1$\left( {{Tx}\quad {power}\quad {to}\quad {the}\quad {MS}} \right) \geq \frac{\begin{matrix}\left( {{total}\quad {available}\quad {at}\quad {BS}\quad {for}\quad {all}} \right. \\\left. {{forward}\quad {link}\quad {in}\quad {the}\quad {same}\quad {FA}} \right)\end{matrix} - \left( {{power}\quad {margin}} \right)}{{number}\quad {of}\quad {MSs}\quad {in}\quad {service}\quad {in}\quad {the}\quad {same}\quad {FA}}$

2 (average reverse link received signal strength (i.e., RSSI) for aparticular duration) ≦ Th_(rssi) − σ_(rssi) 3 (average reverse link SNRfor a particular duration) ≦ Th_(snr) − σ_(snr) 4 any availableorthogonal code?

[0151] In Table 9, condition 1 is satisfied when the transmission powerto the mobile station is higher than or equal to a value obtained bydividing a value:

(total available power at the base station for all forward link in thesame FA)−(a power margin)

[0152] by the number of mobile stations in service in the same area. Thesecond condition (2) is satisfied when an average reverse link receivedsignal strength (i.e., RSSI or Ec/Io of the forward pilot channel), isused in the above case for a particular duration is lower than or equalto a value obtained by subtracting a standard deviation of the RSSI,σ_(rssi) from a threshold RSSI, Th_(rssi). Condition 3 is satisfied whenan average reverse link SNR for a particular duration is lower than orequal to a value obtained by subtracting a standard deviation of theSNR, σ_(snr) from a threshold SNR, Th_(snr). Condition 4 is satisfiedwhen there are available orthogonal codes among the orthogonal codes ofthe requested length. Here, the orthogonal codes are searched for andextracted based on the procedure of FIG. 9. That is, as the result ofthe search, even though there may exist available orthogonal codes, theyare considered as unavailable orthogonal codes when they do not satisfyorthogonality with the other orthogonal codes in use. That is, theorthogonal codes satisfying condition 4 should have a lengthcorresponding to the requested coding rate and have orthogonality withthe forward channel for the other mobile stations.

[0153] To satisfy the first rate change condition, conditions 1 and 4 inTable 9 should be satisfied. Accordingly, when conditions 1 and 4 aresatisfied, the present rate can be changed to the lower rate. However,when conditions 2 and 3 are satisfied while conditions 1 and 4 areunsatisfied, the rate change is not processed when at least 3 conditionsare used for decision criteria. That is, only when conditions 1 and 4are both satisfied, can the present rate be changed to the lower rate.Here, it is assumed that even when one or both of the conditions 2 and 4are satisfied while the conditions 1 and 4 are both satisfied, the firstrate change condition is satisfied.

[0154] Accordingly, when the first rate change condition is satisfied instep 715, the base station sends to the mobile station information aboutthe requested coding rate and the assigned orthogonal code together withthe response message, in step 717. For example, when the ⅓ coding rateis presently used, it can be changed to the ⅙ coding rate, and when the½ coding rate is presently used, it can be change to ¼ coding rate. Inthis case, the shorter orthogonal codes are assigned which have theorthogonality with the orthogonal codes used for the other forward linkchannels. The decision block 213 includes a table for storing theorthogonal codes previously set by the Hadamard transform, and assignsthe orthogonal codes by selecting from the table the orthogonal codeshaving orthogonality with other orthogonal codes based on the procedureof FIG. 9. After sending the changed coding rate and the orthogonalinformation, the decision block 213 of the base station outputs thecoding select signal Csel and the orthogonal code number and lengthsignals Wno and Wlength for changing the present rate to the requestedlower rate in step 719, thereby to change the coding rate and theorthogonal code of the channel encoder in the base station.

[0155] Then, as illustrated in FIG. 3, in the base station, the selector301 outputs the input data to the second encoder 312 and the selector393 outputs the decimated long code from the decimator 392 to the secondmixer 342 according to the coding select signal Csel. Further, thesecond orthogonal modulator 362 multiplies the symbol data output fromthe second encoder 352 by the newly assigned orthogonal code. Therefore,the rate of the orthogonal spread signal applied to the spreader 370 ischanged to the lower rate. In addition, the decision block 213 of themobile station also outputs the received Csel, Wno and Wlength. Thus, asillustrated in FIG. 4, the selector 420 applies the received signaloutput from the despreader 410 to the second orthogonal demodulator 432,which multiplies the despread signal by the newly assigned orthogonalcode. Furthermore, the selector 493 outputs the decimated long code fromthe decimator 492 to the second mixer 452 according to the coding selectsignal Csel, thereby outputting the data decoded in the second decoder482 as the received data.

[0156] However, when the rate change request message represents thechange to the higher rate in step 713, the decision block 213 of thebase station determines in step 721 whether the second rate changecondition is satisfied. Here, the second rate change condition where thebase station increases the rate, represents the conditions shown in thefollowing Table 10. In the present embodiment, it is assumed that thesecond rate change condition is satisfied in the case where at leasttwo, or one, conditions can be set including condition 1 in Table 10 aresatisfied. TABLE 10 Condition Decision 1 (Tx power to the MS) ≦ (averageTx power to all MSs) − σ_(pwr) 2 (average reverse link received signalstrength (i.e., RSSI) for a particular duration) ≧ Th_(rssi) + σ_(rssi)3 (average reverse link SNR for a particular duration) ≧ Th_(snr) +σ_(snr)

[0157] In Table 10, condition 1 is satisfied when transmission power tothe mobile station is lower than or equal to a value obtained bysubtracting a standard deviation, σ_(pwr), of the average transmissionpower for the respective forward traffic channels from an averagetransmission power to all mobile stations. Condition 2 is satisfied whenan average reverse link received signal strength (i.e., RSSI or Ec/Io ofthe forward pilot channel) for a particular duration is higher than orequal to a value obtained by adding the standard deviation of the RSSI,σ_(rssi), to the threshold RSSI, Th_(rssi). Condition 3 is satisfiedwhen an average reverse link SNR for a particular duration is higherthan or equal to a value obtained by adding the standard deviation ofthe SNR, σ_(snr), to the threshold SNR, Th_(snr).

[0158] To satisfy the second rate change condition, condition 1 in Table10 should be satisfied. Accordingly, when condition 1 is satisfied, thepresent coding rate can be changed to the higher coding rate and thelength of the orthogonal code can also be changed after the searchingprocess as described in the algorithm of FIG. 9. However, whenconditions 2 and 3 are satisfied while condition 1 is unsatisfied, thecoding rate and the orthogonal code are not changed. That is, only whencondition 1 is satisfied can the present rate can be changed to thehigher rate. Here, it is assumed that even when one or both of theconditions 2 and 3 are satisfied while condition 1 is satisfied, thesecond rate change condition is satisfied.

[0159] Accordingly, when the second rate change condition is satisfiedin step 721, the base station sends to the mobile station theinformation about the requested coding rate and the assigned orthogonalcode together with the response message, in step 717. For example, whenthe present coding rate is ⅙, the FEC rate can be changed to the ⅓, andwhen the present coding rate ¼, it can be change to ½. In this case, asthe coding rate is increased, the longer orthogonal codes can beassigned which have the orthogonality with the orthogonal codes used forthe other forward link channels. After sending the changed coding rateand orthogonal code, the decision block 213 of the base station outputsthe coding select signal Csel and the orthogonal code number and lengthsignals Wno and Wlength for changing the present rate to the requestedhigher rate in step 719, thereby to change the coding rate and theorthogonal code of the channel encoder in the base station.

[0160] Then, as illustrated in FIG. 3, the selector 301 outputs theinput data to the first encoder 311 and the selector 393 outputs thedecimated long code from the decimator 392 to the first mixer 341according to the coding select signal Csel. Further, the firstorthogonal modulator 361 multiplies the symbol data output from thefirst encoder 351 by the newly assigned orthogonal code. Therefore, therate of the orthogonal spread signal applied to the spreader 370 ischanged to the higher rate. In addition, the decision block 213 of themobile station also outputs the received Csel, Wno and Wlength. Thus, asillustrated in FIG. 4, the selector 420 applies the received signaloutput from the despreader 410 to the first orthogonal demodulator 431,which multiplies the despread signal by the newly assigned orthogonalcode. Furthermore, the selector 493 outputs the decimated long code fromthe decimator 492 to the first mixer 451 according to the coding selectsignal Csel, so that the data decoded in the first decoder 481 isapplied to the receiver as the received data.

[0161] However, when the rate change request message from the mobilestation does not satisfy both the first or second rate changeconditions, the decision block 213 of the base station perceives this instep 715 or 721, and sends to the mobile station a response messageindicating that a change of coding rate and the corresponding orthogonalcode is not possible, in step 723.

[0162] When the rate change request message is not received from themobile station in step 711, the procedure of FIG. 7B is performed todetermine whether or not to change the rate. Also, even when the ratechange request message is received from a particular mobile station, thebase station can perform the procedures of FIGS. 7A and 7B in parallelto determine whether or not to change the rates of the other mobilestations which have not requested the rate change. In FIG. 7B, thedecision block 213 of the base station detects the power consumption ofthe forward traffic channel for the mobile stations and changes therates according to the detection. That is, the decision block 213selects the lower rate for the mobile station which consumes the highpower, and can select the higher rate for the mobile station whichconsumes the low power.

[0163] First, a description will be given as to the rate changeoperation of the mobile station which consumes the high power. Thedecision block 213 of the base station searches for the forward link andthe mobile station which consume the highest power among the forwardlinks using the higher rate encoder, in step 751. The decision block 213determines in step 753 whether the searched mobile station can changethe rate or not by consulting the internal search list. When thesearched mobile station can change the rate, the decision block 213checks in step 755 whether the first rate change condition is satisfiedor not. Here, it is assumed that the first rate change conditionrepresents the case where at least three conditions including theconditions 1 and 4 in Table 9 are satisfied. When the first rate changecondition is unsatisfied, the decision block 213 returns to step 711 torepeat the procedure of FIG. 7B. However, when the first rate changecondition is satisfied in step 755, the decision block 213 of the basestation sends to the mobile station a request message for selecting thelower rate and performs a procedure for decreasing the coding rate ofthe forward channel, in step 757.

[0164] Next, a description will be given as to the rate change operationof the mobile station which consumes the low power. The decision block213 of the base station searches for the forward link and the mobilestation which consume the lowest power among the forward links using thelower rate encoder, in step 759. The decision block 213 determines instep 761 whether the searched mobile station can change the rate or notby consulting the internal search list. When the searched mobile stationcan change the rate, the decision block 213 checks in step 763 whetherthe second rate change condition is satisfied or not. Here, it isassumed that the first rate change condition represents the case whereat least two conditions including the condition 1 in Table 10 aresatisfied. When the second rate change condition is unsatisfied, thedecision block 213 returns to step 711 to repeat the procedure of FIG.7B. However, when the second rate change condition is satisfied in step763, the decision block 213 of the base station sends to the mobilestation a request message for selecting the higher rate and performs aprocedure for increasing the coding rate of the forward channel, in step765.

[0165] However, when the mobile station having the highest powerconsumption or the lowest power consumption can not change the rateduring the call, such as the conventional IS-95 mobile station, thedecision block 213 of the base station perceives this in step 753 or761, and goes to step 767 to delete from the search list the mobilestation which cannot change the rate. After deletion, the decision block213 returns to step 711 to repeat the procedure of FIG. 7B.

[0166] Referring to FIG. 8, in step 811, the decision block 213 of themobile station analyzes the received signal to determine whether therate change request message is received from the base station. When therate change request message is received from the base station in step811, the decision block 213 of the mobile station checks in step 813whether the received rate change request message represents the changeto the higher rate or to the lower rate.

[0167] When the received rate change request message represents thechange to the lower rate in step 813, the decision block 213 of themobile station determines in step 815 whether a first rate changecondition is satisfied or not. Here, the first rate change conditionwhere the mobile station selects the lower rate, represents a case inwhich at least two of the conditions in the following Table 11 aresatisfied. TABLE 11 Condition Decision 1 (average Tx power for aparticular duration) ≧ Th_(pwr) + σ_(pwr) 2 (average forward linkreceived signal strength (i.e., RSSI or forward pilot Ec/Io) for aparticular duration) ≦ Th_(rssi) − σ_(rssi) 3 (average forward trafficchannel SNR for a particular duration) ≦ Th_(snr) − σ_(snr)

[0168] In Table 11, condition 1 is satisfied when an average reversetransmission power for a particular duration is higher than or equal toa value obtained by adding a standard deviation σ_(pwr) to a thresholdpower Th_(pwr). Condition 2 is satisfied when an average receivedforward link RSSI (forward pilot Ec/Io may also be used) for aparticular duration is lower than or equal to a value obtained bysubtracting a standard deviation σ_(rssi) from a threshold RSSITh_(rssi). A condition 3 is satisfied when an average received forwardlink SNR for a particular duration is lower than or equal to a valueobtained by subtracting a standard deviation σ_(snr) from a thresholdSNR Th_(snr).

[0169] Here, it is assumed that at least two conditions out of theconditions 1 to 3 in Table 11 should be satisfied in order to satisfythe first rate change condition. When at least two of the conditions inTable 11 are satisfied, the present coding rate can be changed to thelower rate and the length of the orthogonal code can also be changedaccordingly.

[0170] Accordingly, when the first rate change condition is satisfied instep 815, the mobile station sends to the base station the requestedcoding rate and the assigned orthogonal code together with a responsemessage in step 817, and changes the coding rate and the orthogonal codeaccording to the change rate in step 819 to perform the communicationservice at the changed rate.

[0171] However, when the received rate change request message representsthe change to the higher rate in step 813, the decision block 213 of themobile station examines in step 821 whether a second rate changecondition is satisfied or not. Here, the second rate change conditionwhere the mobile station changes the present rate to the higher rate,represents a condition in which at least two of the conditions in thefollowing Table 12 are satisfied. TABLE 12 Condition Decision 1 (averagereverse Tx power for a particular duration) ≦ Th_(pwr) − σ_(pwr) 2(average forward link received signal strength (i.e., RSSI or Ec/Io ofthe forward pilot) for a particular duration) ≧ Th_(rssi) + σ_(rssi) 3(average reverse link SNR for a particular duration) ≧ Th_(snr) +σ_(snr)

[0172] In Table 12, the condition 1 is satisfied when an average reversetransmission power for a particular duration is lower than or equal to avalue obtained by subtracting a standard deviation, σ_(pwr), of thereverse link from a threshold power Th_(pwr). Condition 2 is satisfiedwhen an average received forward link signal strength (i.e., RSSI orpilot Ec/Io) for a particular duration is higher than or equal to avalue obtained by adding a standard deviation of the RSSI, σ_(rssi), toa threshold RSSI Th_(rssi). Condition 3 is satisfied when an averagereceived forward traffic channel SNR for a particular duration is higherthan or equal to a value obtained by adding a standard deviation of theSNR, σ_(snr), to a threshold SNR Th_(snr).

[0173] Here, it is assumed that at least two of the conditions 1 to 3 inTable 12 should be satisfied in order to satisfy the second rate changecondition. When at least two of the conditions in Table 12 aresatisfied, the present FEC rate can be changed to the higher rate andthe length of the orthogonal code can also be changed accordingly.

[0174] Accordingly, when the second rate change condition is satisfiedin step 821, the mobile station sends to the base station the requestedcoding rate and the assigned orthogonal code together with a responsemessage in step 817. For example, when the present coding rate is ⅙, itcan be changed to ⅓, and when the present coding rate is ¼, it can bechanged to ½. Further, the longer orthogonal code can be assigned afterthe searching process as described in FIG. 9. After sending the changedcoding rate and orthogonal code, the decision block 213 of the mobilestation outputs the coding select signal Csel and the orthogonal codenumber and length signals Wno and Wlength for selecting the requestedhigher rate to change the coding rate of the encoder and the orthogonalcode in step 819, thereby to perform the communication service at thechanged rate.

[0175] However, when the rate change request message received from thebase station does not satisfies both the first and second rate changeconditions, the decision block 213 of the mobile station perceives thisin step 815 or 821, and sends to the mobile station a response messagerepresenting impossibility of changing the coding rate and theorthogonal code in step 823, terminating the procedure.

[0176] As stated above, the base station and the mobile station changethe coding rate and the orthogonal code according to the rate changerequest message or the signal state received from the other party, sothat they can adaptively maintain a good rate according to the channelenvironment. Although FIGS. 7A, 7B and 8 show an embodiment whichchanges both the coding rate and the orthogonal code to change the rate,it is also possible to change the rate by selectively changing thecoding rate or the orthogonal code according to the channel environment.

[0177] The forward traffic channel transmission device of FIG. 3 has thestructure of using a single carrier. However, with the progress of thecommunication technology and service, the subscribers to thecommunication service are increasing in number. Also, there have beenproposed many methods for meeting the subscribers' demands for theservices. As one of the methods, the TIA/EIA TR45.5 conference hasproposed the fundamental channel forward link structure for themulticarrier CDMA system. A method using the multicarrier overlays threeforward link carriers for the multicarrier system on three 1.25 MHzbandwidths used in the IS-95 CDMA system, or selects the three 1.25 MHzbands with one forward channel. In this case, all the three carriersused in the multicarrier system have independent transmission powers.

[0178] Accordingly, when the transmission device of the invention isapplied to the multicarrier system, the decision block 213 of FIG. 2should generate the orthogonal code number and length signals Wno andWlength for generating the orthogonal codes for the multicarrier systemtogether with the coding select signal Csel for selecting the codingrate. Since the respective carriers are independent of one another, theWalsh code number signal Wno output from the decision block 213 shouldalso be able to assign the orthogonal codes as many as the number of thecarriers.

[0179]FIG. 10 illustrates a multicarrier transmission device accordingto another embodiment of the present invention. It is assumed that theforward traffic channel transmission device uses 3 carriers, andincludes a rate ⅓ encoder, a rate 16 encoder and a plurality oforthogonal modulators for independently modulating the signals accordingto the three carriers.

[0180] Referring to FIG. 10, a selector 301 has a first output endconnected to a first encoder 311 and a second output end connected to asecond encoder 312. The selector 301 receives input data to betransmitted and selectively outputs the input data to the first encoder311 or the second encoder 312 according to the select signal Csel outputfrom the decision block 213.

[0181] The first encoder 311, upon reception of the data input from theselector 301, encodes and punctures the input data into data symbols atthe ⅓ coding rate (the first coding rate). That is, the first encoder311 encodes one input data bit into three symbols. A convolutionalencoder or a turbo encoder can be used for the first encoder 311. Afirst symbol repetition part 321 receives the data encoded at the firstcoding rate, and repeats the symbols output from the first encoder 311so as to match the symbol rates of the data having different bit rates.A first interleaver 331 interleaves first encoded data output from thefirst symbol repetition part 321. A block interleaver can be used forthe first interleaver 331.

[0182] The second encoder 312, upon reception of the data input from theselector 301, encodes and punctures the input data into data symbols atthe coding rate ⅙ (the second coding rate). That is, the second encoder312 encodes one input data bit into six symbols. A convolutional encoderor a turbo encoder can be used for the second encoder 312. A secondsymbol repetition part 322 receives the data encoded at the secondcoding rate, and repeats the symbols output from the second encoder 312so as to match the symbol rates of the data having different bit rates.A second interleaver 332 interleaves second encoded data output from thesecond symbol repetition part 322. A block interleaver can be used forthe second interleaver 332.

[0183] A long code generator 391 generates long codes for the useridentification, which are differently assigned to the respectivesubscribers. A decimator 392 decimates the long codes so as to match arate of the long codes to a rate of the symbols output from theinterleavers 331 and 332. A selector 393 selectively outputs thedecimated long code output from the decimator 392 to a mixer 341 or amixer 342 according to the encoder select signal Csel. The selector 393switches the decimated long code to the first mixer 341 to select the ⅓coding rate and to the second mixer 342 to select the ⅙ coding rate. Themixer 341 mixes the first encoded data output from the first interleaver331 with the long code output from the selector 393. The second mixer342 mixes the second encoded data output from the second interleaver 332with the long code output from the selector 393.

[0184] A first demultiplexer 1011 demultiplexes data output from thefirst mixer 341 to the respective carriers in sequence. Signal mappingparts 1021-1023 map levels of the binary data output from the firstdemultiplexer 1011 by converting data “0” to “+1” and data “1” to “−1”.Orthogonal modulators 1031-1033, in the same number as that of thecarriers, each include a first orthogonal code generator (not shown)which generate a first orthogonal code for orthogonally modulating thefirst encoded data according to the orthogonal code number and lengthWno and Wlength output from the decision block 213. The orthogonalmodulators 1031-1033 multiply the first orthogonal code generatedaccording to the orthogonal code number and length Wno and Wlength bythe data output from the signal mapping parts 1021-1023, respectively,to generate a first orthogonal modulation signal. Here, it is assumedthat the Walsh code is used for the orthogonal code and a Walsh code oflength 256 is used for the data encoded at the first coding rate of ⅓.

[0185] A second demultiplexer 1012 demultiplexes data output from thesecond mixer 342 to the respective carriers in sequence. Signal mappingparts 1026-1028 map levels of the binary data output from the seconddemultiplexer 1012 by converting data “0” to “+1” and data “1” to “−1”.Orthogonal modulators 1036-1038, in the same number as that of thecarriers, each include a second orthogonal code generators (not shown)which generate a second orthogonal code for orthogonally modulating thesecond encoded data according to the orthogonal code number and lengthWno and Wlength output from the decision block 213. The orthogonalmodulators 1036-1038 multiply the second orthogonal code generatedaccording to the orthogonal code number and length Wno and Wlength bythe data output from the signal mapping parts 1021-1023, respectively,to generate second orthogonal modulation signals. Here, it is assumedthat the Walsh code is used for the orthogonal code and a Walsh code oflength 128 is used for the data encoded at the second coding rate of ⅙.

[0186] Spreaders 1041-1043 combine the first and second orthogonalmodulation signals output from the orthogonal modulators 1031-1033 andsecond orthogonal modulators 1036-1038 with the received spreadingsequence to spread transmission signals. Here, the PN sequence can beused for the spreading sequence and the QPSK spreaders can be used forthe spreaders. Gain controllers 1051-1053 control gains of the spreadsignals input from the spreaders 1041-1043 according to gain controlsignals G1-G3. The respective gain controllers 1051-1053 outputdifferent carriers.

[0187] As described above, during the call setup or call processing, thebase station and the mobile station change the coding rate and theorthogonal code according to the channel environment, in order toprovide the communication service in the good channel environment. Bychanging the FEC rate for all the link channels of the CDMAcommunication system, it is possible to improve the performance of thereception device and save the transmission power of the transmissiondevice. In addition, it is possible to simply change the rate using themessage.

[0188] While the invention has been shown and described with referenceto a certain preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A channel communication apparatus for a wirelesscommunication system, comprising: a channel receiver for receiving achannel signal; a controller for analyzing the received channel signalto assess a channel environment, said assessment being used by saidchannel receiver to generate a coding rate select signal and orthogonalcode information; and a channel transmitter including: a channel encoderfor adaptively encoding transmission data at a coding rate selectedaccording to the coding rate select signal, and an orthogonal modulatorfor generating an orthogonal code according to the orthogonal codeinformation to spread the encoded transmission data with the generatedorthogonal code.
 2. The channel communication device as claimed in claim1, wherein said controller performs said channel assessment by: (i.)measuring at least one of a receiving power, interference, a bit errorrate (BER) and a signal-to-noise ratio (SNR) from the received channelsignal, (ii.) comparing the measured values with corresponding upperthreshold values to generate the coding rate select signal fordecreasing the coding rate and the orthogonal code information byreducing a length of the orthogonal code when the measured values exceedthe upper threshold values, and (iii.) comparing the measured valueswith corresponding lower threshold values to generate the coding rateselect signal for increasing the coding rate and the orthogonal codeinformation by increasing the length of the orthogonal code when themeasured values are below the lower threshold values.
 3. The channelcommunication apparatus as claimed in claim 1, wherein said channeltransmitter further comprises: at least two channel encoders havingdifferent coding rates, for encoding an input transmission signal at acorresponding coding rate; at least two interleavers for interleavingthe corresponding encoded data by a frame unit; selectors forselectively connecting the input transmission signal to the channelencoders according to the coding rate select signal and selectivelyoutputting an output of the corresponding interleaver; an orthogonalmodulator for generating the orthogonal code corresponding to theorthogonal code information and spreading the encoded data output fromthe selected interleaver with the generated orthogonal code; and apseudo-random noise (PN) spreader for PN spreading the orthogonal spreadsignal.
 4. The channel communication device as claimed in claim 3,wherein said orthogonal code information includes a number and a lengthof the orthogonal code.
 5. The channel communication apparatus asclaimed in claim 1, wherein said channel receiver further comprises: aPN despreader for PN despreading the received signal; an orthogonaldemodulator for generating an orthogonal code corresponding to theorthogonal code information and orthogonally despreading the PN despreadsignal; at least two deinterleavers for deinterleaving the orthogonallydespread signal; at least two channel encoders having different codingrates, for encoding the deinterleaved signal at the correspondingencoding rate; and channel decoders for selectively connecting theorthogonally despread signal to the corresponding deinterleaveraccording to the coding rate select signal and selectively outputting anoutput of the channel encoder having the corresponding coding rate.
 6. Achannel communication apparatus for a wireless communication systemusing multiple carriers, comprising: a channel receiver for receiving achannel signal; a controller for analyzing the received channel signalto assess a channel environment, said assessment being used by saidchannel receiver to generate a coding rate select signal and orthogonalcode information; and a channel transmitter including: a channel encoderfor adaptively encoding transmission data at a coding rate selectedaccording to the coding rate select signal, and an orthogonal modulatorfor generating an orthogonal code according to the orthogonal codeinformation to spread the encoded transmission data with the generatedorthogonal code.
 7. The channel communication device as claimed in claim6, wherein said controller performs said channel assessment by: (i.)measuring at least one of a receiving power, interference, a bit errorrate (BER) and a signal-to-noise ratio (SNR) from the received channelsignal, (ii.) comparing the measured values with corresponding upperthreshold values to generate the coding rate select signal fordecreasing the coding rate and the orthogonal code information byreducing a length of the orthogonal code when the measured values exceedthe upper threshold values, and (iii.) comparing the measured valueswith corresponding lower threshold values to generate the coding rateselect signal for increasing the coding rate and the orthogonal codeinformation by increasing the length of the orthogonal code when themeasured values are below the lower threshold values.
 8. The channelcommunication device as claimed in claim 6, wherein said channeltransmitter comprises: at least two channel encoders each havingdifferent coding rates, for encoding an input transmission signal at thecorresponding coding rate; interleavers for interleaving the encodeddata output from the respective channel encoders, respectively;selectors for selectively connecting the input transmission signal tothe channel encoder having the corresponding coding rate according tothe coding rate select signal and selectively outputting an output ofthe corresponding interleaver; a demultiplexer for demultiplexing theencoded data output from the selectors to the respective carriers;orthogonal modulators for generating the orthogonal code correspondingto the orthogonal code information and spreading the encoded data outputfrom the demultiplexer with the generated orthogonal code; andtransmitters for PN spreading the orthogonal spread signals andtransmitting the PN spread signals by carrying them on the correspondingcarriers, respectively.
 9. The channel communication device as claimedin claim 8, wherein said orthogonal code information includes a numberand a length of the orthogonal code.
 10. The channel communicationdevice as claimed in claim 8, wherein said demultiplexer uniformlydistributes the encoded data to the respective carriers.
 11. The channelcommunication device as claimed in claim 6, wherein said channelreceiver comprises: PN despreaders for frequency shifting the receivedmulticarrier signal using the corresponding carriers and PN despreadingthe frequency-shifted signals; orthogonal demodulators for generatingorthogonal codes corresponding to the orthogonal code information anddespreading the PN despread signals with the corresponding orthogonalcodes; a demultiplexer for demultiplexing outputs of the orthogonaldemodulators; deinterleavers in the same number as that of the codingrates, for deinterleaving the despread signals; at least two channelencoders each having different coding rates, for encoding thedeinterleaved signal at the corresponding encoding rate; and channeldecoders for selectively connecting the orthogonally despread signal tothe corresponding deinterleaver according to the coding rate selectsignal and selectively outputting an output of the channel encoderhaving the corresponding coding rate.
 12. A channel communication methodfor a wireless communication system, comprising the steps of: (i)analyzing an environment of a channel in service, and selecting a codingrate and orthogonal code when the channel environment satisfies a ratechange condition; (ii) generating a message including the selectedcoding rate and the orthogonal code; (iii) sending the message to amobile station; and (iv) upon reception of a response message from themobile station responsive to said message; (v) switching from apresently selected coding rate and presently selected orthogonal code tothe selected coding rate and orthogonal code in a channel transmitter.13. The channel communication method as claimed in claim 12, whereinsaid step of selecting a coding rate comprises the steps of: examining acall condition associated with the mobile station to determine whetherthe rate change condition is satisfied; when a first rate changecondition is satisfied, selecting a coding rate lower than a presentcoding rate of the mobile station and selecting an orthogonal codehaving a length corresponding to the selected coding rate; and when asecond rate change condition is satisfied, selecting a coding ratehigher than a present coding rate of the mobile station and selecting anorthogonal code having a length corresponding to the selected codingrate.
 14. The channel communication method as claimed in claim 13,wherein the first rate change condition is satisfied when a transmissionpower to the mobile station is higher than an average transmission powerof all mobile stations presently in service and orthogonal codescorresponding to the selected coding rate are available.
 15. The channelcommunication method as claimed in claim 14, wherein said averagetransmission power is obtained by subtracting a power margin from amaximum transmission power of the base station, and dividing the resultby the number of mobile stations presently in service.
 16. The channelcommunication method as claimed in claim 13, wherein said step ofselecting an orthogonal code comprises the steps of: selecting anorthogonal code length corresponding to the selected coding rate, andwriting unused orthogonal codes having the selected length in a searchlist; examining a correlation between the orthogonal codes in the searchlist and orthogonal codes longer than the orthogonal codes in the searchlist and deleting those orthogonal codes from the search list notsatisfying orthogonality therebetween; determining whether complementaryorthogonal codes of those undeleted orthogonal codes from said searchlist in use; selecting one of the orthogonal codes from said list whosecomplementary orthogonal code is in use; examining a correlation betweenthe orthogonal codes in the search list and orthogonal codes shorterthan the orthogonal codes in the search list and deleting the orthogonalcodes not unsatisfying the orthogonality therebetween, when there is noorthogonal code whose complementary orthogonal code is in use; andselecting one of the orthogonal codes remaining in the search list afterdeletion.
 17. The channel communication method as claimed in claim 13,wherein the first rate change condition is satisfied when a transmissionpower to the mobile station is higher than an average transmission powerof all mobile stations presently in service, orthogonal codescorresponding to the selected coding rate are available, a receivingstrength of a reverse link is lower than a reference strength value, anda signal-to-noise ratio of the reverse link is lower than a referencesignal-to-noise ratio.
 18. The channel communication method as claimedin claim 13, wherein the second rate change condition is satisfied whena transmission power to the corresponding mobile station is lower than areference average transmission power to other mobile stations.
 19. Thechannel communication method as claimed in claim 13, wherein the secondrate change condition is satisfied when a transmission power to thecorresponding mobile station is lower than a reference averagetransmission power to other mobile stations, a receiving strength of areverse link is higher than a reference strength value, and asignal-to-noise ratio of the reverse link is higher than a referencesignal-to-noise ratio.
 20. A channel communication method for a wirelesscommunication system, comprising the steps of: upon reception of a ratechange request message from a mobile station, selecting a coding rateand orthogonal code according to the rate change request message anddetermining whether there exist available orthogonal codes correspondingto the selected coding rate; generating a response message includinginformation about the selected coding rate and orthogonal code andsending the generated response message to the mobile station initiatingsaid rate change request message; and switching the present coding rateand orthogonal code of a channel transmitter to the selected coding rateand orthogonal code.
 21. The channel communication method as claimed inclaim 20, wherein said step of selecting a coding rate comprises thesteps of: examining a call condition with the mobile station todetermine whether a rate change condition is satisfied; when a firstrate change condition is satisfied, selecting a coding rate lower than apresent coding rate of the mobile station and selecting an orthogonalcode having a length corresponding to the selected coding rate; and whena second rate change condition is satisfied, selecting a coding ratehigher than a present coding rate of the mobile station and selecting anorthogonal code having a length corresponding to the selected codingrate.
 22. The channel communication method as claimed in claim 21,wherein the first rate change condition is satisfied when a transmissionpower to the mobile station is higher than an average transmission powerof all mobile stations presently in service, and orthogonal codescorresponding to the selected coding rate are available.
 23. The channelcommunication method as claimed in claim 22, wherein said averagetransmission power is obtained by subtracting a power margin from amaximum transmission power of the base station and then dividing theresult by the number of the mobile stations presently in service. 24.The channel communication method as claimed in claim 21, wherein saidorthogonal code selection step comprises the steps of: selecting anorthogonal code length corresponding to the selected coding rate, andwriting unused orthogonal codes having the selected length in a searchlist; examining a correlation between the orthogonal codes in the searchlist and orthogonal codes longer than the orthogonal codes in the searchlist and deleting those orthogonal codes from said search list notsatisfying orthogonality therebetween; determining whether complementaryorthogonal codes of those undeleted orthogonal codes from said searchlist are in use; selecting one of the orthogonal codes from said listwhose complementary orthogonal code is in use; examining a correlationbetween the orthogonal codes in the search list and orthogonal codesshorter than the orthogonal codes in the search list and deleting theorthogonal codes not unsatisfying the orthogonality therebetween, whenthere is no orthogonal code whose complementary orthogonal code is inuse; and selecting one of the orthogonal codes remaining in the searchlist after deletion.
 25. The channel communication method as claimed inclaim 21, wherein the first rate change condition is satisfied when atransmission power to the mobile station is higher than an averagetransmission power of all mobile stations presently in service,orthogonal codes corresponding to the selected coding rate areavailable, a receiving strength of a reverse link is lower than areference strength value, and a signal-to-noise ratio of the reverselink is lower than a reference signal-to-noise ratio.
 26. The channelcommunication method as claimed in claim 21, wherein the second ratechange condition is satisfied when a transmission power to thecorresponding mobile station is lower than a reference averagetransmission power to the other mobile stations.
 27. The channelcommunication method as claimed in claim 21, wherein the second ratechange condition is satisfied when a transmission power to thecorresponding mobile station is lower than a reference averagetransmission power to the other mobile stations, a receiving strength ofa reverse link is higher than a reference strength value, and asignal-to-noise ratio of the reverse link is higher than a referencesignal-to-noise ratio.
 28. A channel communication method for a wirelesscommunication system, comprising the steps of: analyzing an environmentof a channel in service to determine whether a rate change condition issatisfied, and sending a rate change request message to a base stationwhen the rate change condition is satisfied; and upon reception of aresponse message from the mobile station in response to said rate changerequest message, switching a presently used coding rate and a presentlyused orthogonal code, of a channel receiver to a coding rate and anorthogonal code corresponding to information included in the responsemessage from the mobile station.
 29. The channel communication method asclaimed in claim 28, wherein the step of determining whether a ratechange condition is satisfied comprises the steps of: examining anenvironment of a channel in communication with the base station;selecting a coding rate lower than a present coding rate, when a firstrate change condition is satisfied; and selecting a coding rate higherthan a present coding rate, when a second rate change condition issatisfied.
 30. The channel communication method as claimed in claim 29,wherein the first rate change condition is satisfied when a conditionselected from the group including: condition 1: an average reverse linktransmission power is higher than an upper threshold transmission power;condition 2: an average forward link receiving strength is lower than alower threshold receiving strength; and condition 3: an average forwardlink signal-to-noise ratio is lower than a lower thresholdsignal-to-noise ratio; is satisfied.
 31. The channel communicationmethod as claimed in claim 29, wherein the second rate change conditionis satisfied when a condition selected from the group including:condition 1: an average reverse link transmission power is lower than alower threshold transmission power; condition 2: an average forward linkreceiving strength is higher than an upper threshold receiving strength;and condition 3: an average forward link signal-to-noise ratio is higherthan an upper threshold signal-to-noise ratio; is satisfied.
 32. Achannel communication method for a wireless communication system,comprising the steps of: upon reception of a rate change request messagefrom a base station, selecting a coding rate and an orthogonal codeaccording to information included in the request message; sending aresponse message to the base station; and changing a presently usedcoding rate and orthogonal code of a channel receiver to the selectedcoding rate and orthogonal code.
 33. A channel communication method fora CDMA communication system, comprising the steps of: (i.) uponreception of a rate change request message from a base station,determining whether a present coding rate and orthogonal code can bechanged to a different coding rate and orthogonal code based oninformation in the request message; (ii.) when the present coding rateand orthogonal code can be changed, changing the present coding rate andorthogonal code to the different coding rate and orthogonal code, andsending a response message to the base station indicating said changes;and (iii.) when the present coding rate and orthogonal code cannot bechanged, generating and sending a message to the base station indicatingthat the change cannot occur.
 34. A channel communication method for aCDMA communication system, comprising the steps of: selecting anorthogonal code length corresponding to a coding rate, and selectingunused orthogonal codes among orthogonal codes having the selectedlength; examining a correlation between the selected unused orthogonalcodes and orthogonal codes longer than the selected orthogonal codes andexcluding orthogonal codes not satisfying orthogonality therebetween;examining a correlation between the selected unused orthogonal codes andorthogonal codes shorter than the selected orthogonal codes andexcluding orthogonal codes not satisfying orthogonality therebetween;assigning one of the selected unused orthogonal codes remaining afterexclusion.
 35. A channel communication method for a wirelesscommunication system, comprising the steps of: selecting an orthogonalcode length corresponding to a coding rate, and selecting unusedorthogonal codes among the orthogonal codes having the selected length;examining a correlation between the selected unused orthogonal codes andorthogonal codes longer than the selected orthogonal codes and excludingorthogonal codes not satisfying orthogonality therebetween; determiningwhether complementary orthogonal codes of the orthogonal codes remainingafter exclusion are in use; and assigning one of the selected unusedorthogonal codes whose complementary orthogonal codes are in use. 36.The channel communication method as claimed in claim 35, wherein saidcomplementary orthogonal code is determined by (i+N/2)mod N (where i isan orthogonal code number and N is an orthogonal code length.
 37. Thechannel communication method as claimed in claim 35, further comprisingthe steps of: when the complementary orthogonal codes corresponding tothe orthogonal codes remaining after exclusion are all not in use,examining a correlation between the remaining orthogonal codes andorthogonal codes shorter than the remaining orthogonal codes andexcluding the orthogonal codes not satisfying orthogonalitytherebetween; and assigning one of the orthogonal codes remaining afterexclusion.